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An artist’s depiction of the OSIRIS-REx spacecraft touching down on the asteroid Bennu. 

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ASA’s OSIRIS-REx spacecraft last week conducted its final sample retrieval rehearsal on the asteroid Bennu, some 170 million miles from Earth. This four-hour rehearsal was in preparation for the spacecraft’s attempt at collecting dust and rocks from the surface of the asteroid in October. If successful, OSIRIS-REx will be the first American spacecraft to bring samples of an asteroid back to Earth.

This final rehearsal, conducted on Tuesday, Aug. 11, involved the spacecraft testing its sampling acquisition system, collecting data from the asteroid’s surface, moving solar panels and using its thrusters as it orbits the rock.

During the rehearsal, the OSIRIS-REx spacecraft passed 144 feet above the asteroid’s surface—the closest it’s ever come. From that close proximity, the spacecraft’s camera suite captured its highest quality images yet. 

The mission has been a center of attention here in Tucson, as its principal investigator is Dante Lauretta, a professor of planetary science and cosmochemistry at the University of Arizona’s Lunar and Planetary Laboratory. Multiple other researchers from UA are also involved with the mission.

According to NASA, because the spacecraft is millions of miles from Earth, it takes approximately 16 minutes for the spacecraft to receive the radio signals used to command it. This time lag prevented live commanding of flight activities from the ground during the rehearsal. As a result, the spacecraft performed the entire rehearsal sequence autonomously. Prior to the rehearsal’s start, the OSIRIS-REx team uplinked all of the event’s commands to the spacecraft and then provided the “Go” command to begin the event. The actual sample collection event in October will be conducted the same way.

OSIRIS-REx will not land on Bennu’s surface to capture its sample. Instead, it will use the Touch-And-Go (TAG) Sample Acquisition Mechanism to shoot a jet of nitrogen, dislodging particles from the asteroid. The spacecraft is expected to be able to capture upwards of 60 grams worth of carbonaceous dust and rock ejected from Bennu’s surface.

The OSIRIS-REx spacecraft launched from the Earth in September 2016 and is planned to return in 2023. The spacecraft, part of a NASA program, will collect rocks and dust from the surface of Bennu in order to better understand “the initial stages of planet formation and the source of organic compounds available for the origin of life.” Since arriving at Bennu in December 2018, OSIRIS-Rex has mapped the asteroid’s rocky and carbon-rich surface.

Prior to sample collection, researchers have already learned a lot about Bennu, including that it is one of the darkest objects in the solar system, it is packed with more than 200 boulders larger than 33 feet in diameter, and hydrated minerals on its surface indicate it encountered water at some point in its past. 

Its extremely rugged terrain will make the sample acquisition more difficult than previously anticipated. However, the OSIRIS-REx team has selected a potential site, named “Nightingale,” that is comparatively less hazardous. 

“Many important systems were exercised during this rehearsal—from communications, spacecraft thrusters, and most importantly, the onboard Natural Feature Tracking guidance system and hazard map,” Lauretta said. “Now that we’ve completed this milestone, we are confident in finalizing the procedures for the TAG event. This rehearsal confirmed that the team and all of the spacecraft’s systems are ready to collect a sample in October.”

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